The present invention relates to the fabrication of integrated circuits, particularly to the formation of nuclear tracks in a patterned mask layer, and more particularly to the formation of wide tracks (100-200 nm) in nuclear trackable material without causing delamination of the material.
The formation of holes, openings, or passages in dielectric materials has involved directing high-energy charged particles onto the material thereby forming latent nuclear tracks in the dielectric material, followed by etching. The passage of an atomic particle through a dielectric material can result in the creation of a latent nuclear track that extends along a straight line corresponding to the path of the atomic particle. This latent track has a diameter of 5-30 nm with bonding and density different from the non-tracked regions. Various methods for forming tracks in nuclear trackable materials have been developed, as exemplified by U.S. application Ser. No. 08/851,258 filed May 5, 1997, entitled "Vapor Etching of Nuclear Tracks in Dielectric Materials", and U.S. application Ser. No. 08/847,085 filed May 1, 1997, entitled "Use of a Hard Mask for Formation of Gate Dieclectric Via Nanofilament Field Emission Devices", each assigned to the same assignee.
Nuclear tracks can be selectively etched in Nuclear trackable materials, such as polycarbonate, exemplified by LEXAN, made by the General Electric Company. In the case of LEXAN, the track is etched with high selectivity, having diameters as small as 30 nm. In order to etch the track wider, on the order of 100-200 nm, which is desirable for field emitter gate structures, the etch becomes nonselective, and the film is eroded away as the track widens. In order to etch the nuclear track wider, an etch is necessary which will not attack the interface between the LEXAN and the gate metal, so as to prevent delamination of the LEXAN film.
Nuclear tracks in LEXAN are conventionally etched using a KOH or NaOH chemistry. These solutions will also readily etch many metal oxides, including Mo-oxide and W-oxide, which form on the surface of metal exposed to air. As a result, the LEXAN-metal interface is etched somewhat selectively, with the result being delamination of the LEXAN film prior to etching to the required diameter.
The present invention provides a solution to widening the tracks in dielectric materials, particularly LEXAN, to &gt;200 nm without delamination of the film. The invention utilizes an adhesion film which allows the track to be sufficiently widened. The adhesion film is composed of a metal having an inert oxide, or a dielectric having a stable surface. The adhesion film is deposited on top of the gate metal layer or film, or if the properties of the gate metal layer are adequate (have an inert oxide) the gate metal will function as to adhesion film to enable the tracks to be etched to the required diameter without delamination problems.